Significant research has been conducted in recent years on the use of biological agents to increase agricultural productivity and efficiency. Biological control based on the use of microorganisms to suppress plant pests or supplement plant growth offers an attractive alternative to chemical pesticides which are less favored than they have previously been because of concerns about human health and environmental quality. Several screening programs have been used before to isolate biological agents which are effective in the laboratory or in the field to combat pests or facilitate plant growth.
An example of a biological control agent into which significant scientific and economic development has occurred is the use of the Bacillus thuringiensis. It was recognized that B. thuringiensis strains produced toxic proteins which have the ability to specifically kill certain insects and that initial inquiry led to a significant research which has proceeded to identify a large number of B. thuringiensis strains having variations and target range in efficacy. In addition, research has been conducted on methods for stabilizing and applying such toxins, or strains harboring them, to a wide variety of field crop situations. It was also discovered that knowledge of B. thuringiensis strains was largely transferable to new strains since the toxins required for biological control and methods for preparing inocula for use in the field were generally similar among strains.
Previously it has been found that a specific strain of Bacillus cereus, which has been referred to both as UW85 and by its ATCC designation 53522 has biocontrol efficacy in many applications. The UW85 B. cereus strain was found to protect alfalfa seedlings from damping off caused by Phytophthora medicaginis, tobacco seedlings from Phytophthora nicotianae cucumber fruits from rot caused by Pythium aphanidermatum, and peanuts from Sclerotinia minor. UW85 is also described, by reference to its ATCC number in U.S. Pat. No. 4,877,738. It was later found that UW85 produced two antifungal compounds which contribute independently to its suppression of damping off fungi due to antifungal and antibacterial activity. The more potent of these compounds, a novel aminopolyol has been designated zwittermicin A while the second compound, not well characterized, has been provisionally designated antibiotic B.
"Biological control" is defined as pathogen suppression by the use of a second organism. Mechanisms of biological control are diverse. For example, certain enteric bacteria have been examined for their usefulness in biological control of root rot in alfalfa. It is believed that control is obtained by competition between the enteric bacteria and the fungi for space on the surface of the alfalfa roots. In contrast, a toxin produced by one species of bacteria may be used to control another species of bacteria that appears as a pathogen. Bacterially produced antibiotics are an example of such toxins. The toxin can be isolated from the species producing it and administered directly, as is the common procedure with penicillin, or the species itself may be administered under appropriate circumstances to produce the toxin in situ. Once identified, such toxins produced by soil-dwelling bacteria may have utility in diverse other areas as antifungal or antibiotic agents.